Moisture control device for concrete mixers



Sep 1958 M. E. POSEY ETAL MOISTURE CONTROL DEVICE FOR CONCRETE MIXERSFiled Dec. 5, 1952 INVENTORS. MILTON 5. POSEY MES L.

SAR ENT JR. (Eb/Q W W ATTORNEY MOISTURE CONTROL DEVICE FOR CONCRETEMIXERS :Milton E. Pusey, College Park, and James L. Sargent, Jr.,Decatur, Ga.

ApplicationDecember 5, 1952, Serial No. 324,230 40mins. cram-655 Thisinvention relates to a moisture control device for concrete mixers, andmore particularly to a device for ascertaining and controlling theamount of water added to a batch of concrete being commingled therewithin a mixer.

Since the sand and gravel which are ingredients of concrete are handledand shipped in the open, the water content thereof continually varies,thus rendering it difficult to estimate the amount of water contained bythis sand or gravel at the time it is placed in a concrete mixer. Hence,it is equally diificult to estimate the proper amount of water tobeadded in making a batch of concrete. This problem is most acute whenitis desired to manufacture a semi-dry mix.

In the past, devices have been built which attempt to measure theelectrical resistivity .ofmatenal in a con-' crete mixer, but thesedevices 'have not ,proved satisfactory since the resistivity of theelectrodes themselves vary to such a degree that the reading obtained bythe prior art devices were unreliable. This unreliability is especiallytrue in machines mixingthe so-called wet mix concrete.

The concrete industry has long needed and searched for a positive andpractical method for determining the amount of water which is in .amixture at all times during the process of mixing of concrete.

Accordingly, it is an object of our invention to provide a concretemixer with a moisture indicating and control device which will feedwater into the mixer until the proper moisture content of the concretebatch is attained.

Another object of our invention is to provide an automatic moisturecontrol .andindicator device in combination with a concrete mixingmachine wherein the electrodes of the device are continually cleaned sothat a substantially accurate reading may be obtained therefrom at anytime. 1

Another object of our invention is to provide a sensitive moistureindicator and control device which is simple in design, durable instructure, dependable in operation and economical to maintain.

Other and further objects and advantages of our invention will becomeapparent from the following 'description when taken in conjunction withthe accompanying drawings wherein like characters of reference designatecorresponding parts throughout the several views, and wherein:-

Fig. 1 is an isometric view of an automatic mixing machine with amoisture control device constructed in accordance with .our invention.

Fig. 2 is a wiring diagram of a moisture indicating device whichisadapted to be incorporated in the machine illustrated in Fig. 1.

Fig. 3 .is a schematic wiring diagram of the moisture indicator andcontrol mechanism incorporated with the mixing machine .illustrated inFig. 1.-

Fig. .4 is an enlarged cross-sectional view of a .detail showing thepositioning of the electrodes.

United States Patent 0 Fig. 5 is a view ofa detailshowing the blade .ofthe machine illustrated in Fig. .1.

Referring now in detail 'to the embodiment chosen for purpose ofillustration, numeral 10 denotes a platform supporting'a concrete mixingmachine of the rotary blade type having a cylindrical outer housing .11[provided with ends 12 12'. Housing 11 is provided with an inner liner13, and a shaft 14 is supported axially by ends 12, 12 .so as to bedriven by a motor (not shown) in motor box 15. Helical blades 16connected to shaft 14 are positioned to sweep adjacent lining ,1-3 asshaft 14 is rotated.

To the prior art machine described above, we have provided an insulatingedge 17 along the outer edges of blades 16 as morereadiiy seen in Fig.5. Thisinsulating edge is preferable, when .our concrete mixer is usedfor mixing .a wet mix, but may be eliminated when our machine ,is used.for mixing a semi-dry mix, .the function thereof being described indetaillater. Along the top of housing ,11.is a transverse sprinkler pipe18 which is supported by ends .12, 12' and through which water may beadded to a batch of concrete .within .the mixer. For supplying water topipe 18, We have provided a control valve 19,.connected to pipe 18through flexible hose 20, water being supplied to valve .19 .by waterinlet pipe 21. -It is to be understood that water. inlet valve 19 mayeither ..be manually operated or magnetically operated depending onwhether or not the moisture indicating device as illustratedschematicallyiin Fig. 2 or the moisture control and indicating device asillustratedschematically in Fig. 3 'is used.

In Fig. .l, numeral 22 denotes a cabinet containing the moistureindicator and control device illustrated schematically in Fig. 3 and 'isshown as comprising .an on-oif switch .23, a pilot light 2.4, .amoisture indicating meter 25, a moisture cut-off regulator 26 and a.zero shunt adjustment .27. It should be pointed out that the indicatingdevice illustrated schematically in Fig. 2 may be mounted in place ofthe device in Fig. 3.

A cable .28 having two wires, leads from panel :22 and each wire isrespectively connected to pairs .ofelectrodes 29 and 30 locatedcentrally on the lower portion of housing 11. As seen more clearly inFig. 4, electrodes 29 and 30, respectively, extend through insulatingbushings .31 and 32 and :terminate in wide flat heads which are flushwith the inside periphery of lining 13. Nuts 33 and 34 are respectivelythreaded tothe portions of electrodes 29 and .30 which extend outsidehousing 11, and insulating washers 35 and 36 between these nuts andhousing 11 prevent electrical short circuiting of the electrodes.

Itisapparent from the foregoing description that when our mixing machineis .in operation, blades 16 will pass adjacent electrodes .29 .and .30thereby preventing .faulty readings due .to .caking of the concretemixin .thearea of the .electrodes. Asdescribed above, when a so-called wetmix" is .being prepared, it is preferable .to provide finsulating edges17 for blades 16 so .that edges 17 will wipe against electrodes 29and-30to prevent caking whichis more pronounced as-the moisture contained.thereinis .increased.

Indicating device Since the electrical resistivity of the concretemix'within the mixer is a function of the moisture content of that mix,as .illustrated schematically in Fig. 2 We .have connected electrodes 29and 30 to the cathode and grid of a triode tube 37 with a condenser .38shunted acrossthe electrodes to minimize current oscillation. 'Byproviding substantially constant potential between plate and grid of.tube .37., the resistiv,it;y of the concrete mix may be read as afunction of the current flowing between the cathode and the plate;therefore, we have provided a circuit comprising an on-otf switch 39which feeds alternating current to transformer 49. In order to obtainsubstantially constant D.-C. potential from transformer 40, we haveprovided a rectifier 41 in series with an R-C filter 42 and whose outputvoltage is regulated by voltage regulator 43, across the D.-C. output.The positive lead of this circuit is connected to the plate of tube 37through an ammeter consisting of a variable shunt 44 in parallel with agalvanometer 45. The negative side of this circuit leads to the gridwhich in turn renders electrode 39 negative. The filament of tube 37 isheated in conventional manner with pilot light 46 being provided in thatcircuit to indicate that the device is operating.

Now it can be seen that when our machine is placed in operation andswitch 39 is closed to provide current to our circuit, the grid bias issufliciently negative to allow substantially no current to pass in themain circuit, thus the ammeter will not register. However, as liquid isadded to the mix, the grid bias becomes less negative and allows currentto pass in the circuit thus giving a reading on the ammeter. It canreadily be seen therefore that by calibrating galvanometer 45 withrespect to the percentage of water in the concrete mix, the indicatingdevice disclosed can easily be used to determine the proper amount ofwater in the concrete mix.

Indicator and control device In order to automatically control valve 19,we have provided a circuit illustrated schematically in Fig. 3 which isresponsive to the percentage of moisture in the concrete mix to therebyopen or shut valve 19. In this circuit, on-ofl? switch 23, when closedfurnishes current to transformers 47 and 47, each respectively havingrectifiers 48 and 49 as well as R-C filters and voltage regulators 50and 51. Therefore, it can be seen that substantially constant D.-C.potential is provided by these two transformers.

As illustrated, transformer 47 furnishes current for triode 52 with thegrid of this triode being connected to electrode 30 and also thenegative side of the circuit, through ground. The positive side of thecircuit, on the other hand, is connected to the plate of triode 52through an ammeter and a potentiometer, the ammeter consisting 'ofmoisture indicating meter 25 and a zero shunt adjustment 27 in parallel,the potentiometer being moisture cut-otf regulator 26. Electrode 29 isconnected to the cathode of the triode 52 with the filament being heatedin conventional manner. Therefore, it is apparent that a negative biasexists between the grid and cathode of triode 52 and that this negativebias will decrease as the resistivity of the concrete mix decreases andcurrent will pass in the circuit, thus giving an indication on meter 25which is a function of the amount of moisture in the concrete mix.

Looking now at the circuit connected with transformer 47, it is seenthat the cathode of a second triode 53 is connected to the negative sideof this circuit while the plate of triode 53 is connected through relay54 and start switch 55 to the positive side of the circuit. As seen,start switch 55 is normally open; therefore, current will not normallypass in this circuit until switch 55 is closed at which time switches 56and 57 will be closed by relay 54, provided current is passing throughtriode 53. Thus, assuming that current is passing in triode 53, whenswitch 55 is depressed, current will continue to pass even though startswitch 55 is then opened. Current will pass through switch 55 which isheld closed by relay 54. Referring to potentiometer 26, it is seen thatthe positive side of transformer 47 and the negative side of transformer47' form a common lead through this potentiometer and that a center tapfrom the potentiometer leads to the grid of triode 53. Therefore, it maybe seen that the grid of triode 53 will normally be negative withrespect to the cathode of that tube; thus, current will normally passwithin tube 53. It should be remembered,

mixer, the current flowing through triode 52 will oppose the currentflowing in tube 53 and thus increase the negative basis of the grid intube 53, thereby decreasing the current flowing through relay 54 untilthis relay opens. It is apparent that by varying the positioning of thetap on potentiometer 26, that the amount of current flowing in tube 53which would cause relay 54 to open, may be varied. An examination ofFig. 3 will indicate that switch 57 which is closed by the closing ofrelay 54 operates to close a circuit furnishing current to magneticcontrol 58 which in turn opens valve 19.

It is apparent from the foregoing description that when on-ofl switch 23.is closed, and start switch .55 depressed, valve 19 will be openeduntil the resistance of the concrete mixdrops to a predetermined pointat which time magnetic control 58 will no longer be actuated and thusallow valve 19 again to close under spring pressure.

In event that valve 19 does not operate automatically as describedabove, bypass switch 59 which will furnish current directly to control58, may be closed to open valve 19.

It will be obvious to those skilled in the art that many variations maybe made in the embodiment chosen for purpose of illustration withoutdeparting from the scope of our invention as disclosed by the followingclaims.

We claim:

1. A moisture indicating device for aggregate mixers of the type havinga stationary casing and rotating agitator blades, said device comprisinga plurality of electrodes extending through the central portion of saidcasing, said electrodes being provided with wide flat heads which areflush with the inner periphery of said casing, insulating bushingsbetween said casing and said electrodes, said blades being positioned tosweep over said electrodes, a triode electronic tube, the cathode ofsaid triode being electrically connected to certain of said electrodes,the grid of said triode being connected to other of said electrodes, anammeter in series with the plate of said triode and calibrated toindicate percentage of moisture in aggregates contacting saidelectrodes, means providing substantially constant direct current to theplate of said triode through said ammeter and also to the grid of saidtriode, and a condenser electrically connected between said electrodesto prevent rapid cur rent fluctuation of current between saidelectrodes.

2. The device as claimed in claim 1 wherein insulating edges areprovided on said agitator blades to wipe the heads of said electrodes assaid blades rotate.

3. A moisture indicating device for aggregate mixers of the type havinga stationary casing and rotating agitator blades, said device comprisinga plurality of electrodes extending through a Wall of said casing, saidelectrodes being provided with heads which are substantially flush withthe inside periphery of said casing, in sulating bushings between saidcasing and said electrodes, a triode electronic tube, the cathode ofsaid triode being electrically connected to certain of said electrodes,the grid of said triode being connected to other of said electrodes, anammeter in series with the plate of said triode and calibrated toindicate percentage of moisture in aggregates contacting saidelectrodes, means providing substantially constant direct current to theplate of said triode through said ammeter and also to the grid of saidtriode, and insulating edges on' said agitator blades to wipe the headsof said electrodes as said blades rotate.

4. A moisture indicating device for aggregate mixers of the type havinga stationary casing and rotating agitator blades therein, said devicecomprising a plurality of electrodes extending through a wall of saidcasing to contact aggregates therein, said electrodes being providedwith heads which are substantially flush with the inner periphery ofsaid casing, insulating bushings between said casing and saidelectrodes, an electrical circuit including an ammeter connected to saidelectrodes, said ammeter being calibrated to indicate percentage ofmoisture in aggregiates contacting said electrodes, and insulating edgeson said agitator blades to Wipe the heads of said electrodes as saidblades rotate.

References Cited in the file of this patent UNITED STATES PATENTS1,930,831 Webb Oct. 17, 1933 6 Polin Sept. 24, 1935 Fisher et a1. Oct.8, 1935 Elberty June 23, 1936 Chapin Ian. 21, 1947 McBrayer May 10, 1949Clardy et al Aug. 21, 1951 Kline Feb. 19, 1952 Elam Apr. 22, 1952

